Conventionally, the drive axle that requires a large steering angle such as the one used for an agricultural tractor most commonly uses a constant velocity style double Cardan joint for connecting a differential output shaft to a wheel. The double Cardan joint has a long axis and a large outside diameter, but its intersecting angle can be as large as more than 50°. A double Cardan joint has two cross shafts (spiders), and uses a total of eight bearings with needle rollers, four each per a spider, set in the journals of each spider. The bearing is composed of rollers arranged in a full complement manner without a retainer, a square U-shaped outer ring, and an oil seal that seals the roller surfaces.
Grease is filled inside the bearing as a lubricant. Because of small volume of space around the rollers, the grease needs to be replenished as required. Failure of grease replenishment at appropriate times will lead to wear of spider journals due to lack of grease and the spiders cannot satisfy their designed durability performance requirements. For this reason, the joint has a structure in which a grease nipple is provided at one location in the center of the spider, so that grease supplied from this nipple is fed to the internal of each bearing through a grease supply hole of each journal of the spider.
However, a double Cardan joint has four bearing (journal) parts in one spider. A supply of grease from one grease nipple can hardly reach all of the four bearing parts evenly and sufficiently. Some Cardan joints, therefore, include a grease nipple in the outer ring of each bearing, so that the lubricant is given evenly and sufficiently to all four bearings. In this case, however, nipples must be provided to the total of eight locations (four nipples per one spider) for the entire joint, which means grease supply is time-consuming.